[TFLite] Add rewrite pattern to fuse conv ops with Relu6 op
[TFLite] Add rewrite pattern to fuse conv ops with Relu6 op

* Fixed tfl.conv_2d and tfl.depthwise_conv_2d to have fused activation
  function attribute
* Fixed RewriterGen crash: trying to get attribute match template when
  the matcher is unspecified (UnsetInit)

PiperOrigin-RevId: 233241755

Intel-Corporation/tensorflow,aam-at/tensorflow,davidzchen/tensorflow,tensorflow/tensorflow-pywrap_tf_optimizer,adit-chandra/tensorflow,arborh/tensorflow,Intel-Corporation/tensorflow,karllessard/tensorflow,adit-chandra/tensorflow,gunan/tensorflow,renyi533/tensorflow,tensorflow/tensorflow-pywrap_saved_model,paolodedios/tensorflow,adit-chandra/tensorflow,DavidNorman/tensorflow,sarvex/tensorflow,aam-at/tensorflow,arborh/tensorflow,gautam1858/tensorflow,jhseu/tensorflow,ppwwyyxx/tensorflow,tensorflow/tensorflow-experimental_link_static_libraries_once,tensorflow/tensorflow-experimental_link_static_libraries_once,xzturn/tensorflow,arborh/tensorflow,yongtang/tensorflow,tensorflow/tensorflow-pywrap_saved_model,DavidNorman/tensorflow,aam-at/tensorflow,davidzchen/tensorflow,paolodedios/tensorflow,frreiss/tensorflow-fred,frreiss/tensorflow-fred,frreiss/tensorflow-fred,gunan/tensorflow,freedomtan/tensorflow,tensorflow/tensorflow-experimental_link_static_libraries_once,tensorflow/tensorflow-experimental_link_static_libraries_once,ppwwyyxx/tensorflow,frreiss/tensorflow-fred,aam-at/tensorflow,tensorflow/tensorflow-experimental_link_static_libraries_once,ppwwyyxx/tensorflow,sarvex/tensorflow,adit-chandra/tensorflow,gautam1858/tensorflow,tensorflow/tensorflow-pywrap_tf_optimizer,aldian/tensorflow,tensorflow/tensorflow,petewarden/tensorflow,ppwwyyxx/tensorflow,xzturn/tensorflow,DavidNorman/tensorflow,arborh/tensorflow,adit-chandra/tensorflow,gunan/tensorflow,aldian/tensorflow,cxxgtxy/tensorflow,ppwwyyxx/tensorflow,tensorflow/tensorflow-pywrap_tf_optimizer,gautam1858/tensorflow,tensorflow/tensorflow,freedomtan/tensorflow,cxxgtxy/tensorflow,Intel-tensorflow/tensorflow,aldian/tensorflow,yongtang/tensorflow,jhseu/tensorflow,tensorflow/tensorflow-pywrap_saved_model,gautam1858/tensorflow,karllessard/tensorflow,sarvex/tensorflow,tensorflow/tensorflow,jhseu/tensorflow,frreiss/tensorflow-fred,tensorflow/tensorflow-experimental_link_static_libraries_once,annarev/tensorflow,Intel-Corporation/tensorflow,petewarden/tensorflow,karllessard/tensorflow,arborh/tensorflow,DavidNorman/tensorflow,karllessard/tensorflow,aam-at/tensorflow,gautam1858/tensorflow,renyi533/tensorflow,paolodedios/tensorflow,arborh/tensorflow,davidzchen/tensorflow,yongtang/tensorflow,frreiss/tensorflow-fred,yongtang/tensorflow,gunan/tensorflow,freedomtan/tensorflow,adit-chandra/tensorflow,gunan/tensorflow,aldian/tensorflow,tensorflow/tensorflow,sarvex/tensorflow,aldian/tensorflow,yongtang/tensorflow,frreiss/tensorflow-fred,karllessard/tensorflow,Intel-tensorflow/tensorflow,arborh/tensorflow,tensorflow/tensorflow,Intel-tensorflow/tensorflow,gunan/tensorflow,tensorflow/tensorflow,xzturn/tensorflow,frreiss/tensorflow-fred,aam-at/tensorflow,DavidNorman/tensorflow,renyi533/tensorflow,petewarden/tensorflow,tensorflow/tensorflow-pywrap_tf_optimizer,adit-chandra/tensorflow,tensorflow/tensorflow-experimental_link_static_libraries_once,tensorflow/tensorflow-pywrap_saved_model,petewarden/tensorflow,cxxgtxy/tensorflow,renyi533/tensorflow,xzturn/tensorflow,gautam1858/tensorflow,petewarden/tensorflow,gunan/tensorflow,aam-at/tensorflow,sarvex/tensorflow,petewarden/tensorflow,jhseu/tensorflow,freedomtan/tensorflow,davidzchen/tensorflow,xzturn/tensorflow,jhseu/tensorflow,ppwwyyxx/tensorflow,tensorflow/tensorflow-experimental_link_static_libraries_once,DavidNorman/tensorflow,xzturn/tensorflow,davidzchen/tensorflow,gunan/tensorflow,DavidNorman/tensorflow,renyi533/tensorflow,petewarden/tensorflow,tensorflow/tensorflow-pywrap_saved_model,yongtang/tensorflow,annarev/tensorflow,freedomtan/tensorflow,tensorflow/tensorflow-pywrap_tf_optimizer,tensorflow/tensorflow-experimental_link_static_libraries_once,adit-chandra/tensorflow,tensorflow/tensorflow-experimental_link_static_libraries_once,davidzchen/tensorflow,gunan/tensorflow,annarev/tensorflow,DavidNorman/tensorflow,karllessard/tensorflow,yongtang/tensorflow,DavidNorman/tensorflow,gautam1858/tensorflow,paolodedios/tensorflow,sarvex/tensorflow,gautam1858/tensorflow,paolodedios/tensorflow,adit-chandra/tensorflow,davidzchen/tensorflow,freedomtan/tensorflow,yongtang/tensorflow,xzturn/tensorflow,Intel-tensorflow/tensorflow,ppwwyyxx/tensorflow,paolodedios/tensorflow,aam-at/tensorflow,aam-at/tensorflow,xzturn/tensorflow,ppwwyyxx/tensorflow,davidzchen/tensorflow,DavidNorman/tensorflow,aldian/tensorflow,ppwwyyxx/tensorflow,DavidNorman/tensorflow,freedomtan/tensorflow,gautam1858/tensorflow,freedomtan/tensorflow,tensorflow/tensorflow-pywrap_saved_model,cxxgtxy/tensorflow,tensorflow/tensorflow-pywrap_tf_optimizer,petewarden/tensorflow,tensorflow/tensorflow-pywrap_saved_model,tensorflow/tensorflow,Intel-tensorflow/tensorflow,gautam1858/tensorflow,aam-at/tensorflow,paolodedios/tensorflow,aam-at/tensorflow,renyi533/tensorflow,adit-chandra/tensorflow,frreiss/tensorflow-fred,xzturn/tensorflow,paolodedios/tensorflow,yongtang/tensorflow,renyi533/tensorflow,xzturn/tensorflow,petewarden/tensorflow,freedomtan/tensorflow,cxxgtxy/tensorflow,arborh/tensorflow,arborh/te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